In the manufacture of plastic parts by injection molding, in order to uniformly direct molten plastic to form parts, it is often desirable to flow the molten plastic through a runner system for feeding the molten plastic into a mold cavity along an elongated edge portion of the part.
In the past, various proposals have been suggested for degating side gate runners from plastic parts during the molding process. In U.S. Pat. No. 5,069,832, high frequency vibration is applied to a mold punch after a gate has been sealed and wherein the vibrational energy softens the plastic around the gate to degate the solidified part while in the mold.
U.S. Pat. No. 4,647,275 discloses a runner shearing assembly that includes a cylindrical sleeve having a punch directed therethrough for shearing a runner from a part. However, in this arrangement, the punch has the shape of the cylinder so as to shear a runner from the part. The gate portion between the shear pin and the cylinder is retained on the part and broken therefrom at a pin-shaped gate during the ejection of a solidified part from the mold.
While the aforesaid degating apparatus and methods are suitable for their intended purpose with the shaped parts illustrated in the aforesaid patents, such in-mold degating assemblies and method are not suited for the manufacture of injection molded parts having side gate runner systems and including a gate portion for feeding molten plastic material into a mold cavity along a long longitudinal edge portion of the part. Such parts often have an aspect ratio greater than 1:1 wherein the runner is connected to an extended length of one side of the solidified part. In order to trim the runner, an operator must knife cut, in a repetitive manner, runners from the side edge of the parts. Such repetitive cutting steps can cause undesirable edge nicks leading to excessive scrap. Additionally, repetitive cutting operations are a known cause of carpal tunnel syndrome.